1. Field of the Invention
The invention relates to an apparatus for the manufacture of compound pipes wherein mould halves, which are provided with annular mould recesses and of which two at a time are combined as a pair on a moulding path to form one mould, are arranged to be guided in a circuit and in a direction of production, wherein the mould recesses are connected to partial vacuum ducts formed in the mould halves, wherein an injection head of at least one extruder is arranged upstream of the moulding path, wherein the injection head is provided with an external nozzle for extrusion of an external tube, and, arranged downstream in direction of production, with an internal nozzle located inside the moulding path for extrusion of an internal tube, and with a cooling and calibrating mandrel arranged downstream at a rear end of the injection head in direction of production.
2. Background Art
Such an apparatus is known for example from U.S. Pat. No. 5,320,797. This known apparatus is used for the manufacture of compound pipes with a circular cross-section consisting of a smooth cylindrical internal tube and a corrugated external tube which are manufactured by co-extrusion. Such compound pipes with an oval cross-section thus cannot be easily manufactured from thermoplastic polymer. Such known oval compound pipes are for example used for the transport of air and similar media. They are particularly applicable for heating, ventilation and air conditioning systems or for electrical installations. Although the apparatus of the generic kind cannot be easily used for the manufacture of such oval compound pipes, the compound pipes manufactured on such apparatuses have the great advantage of possessing a high internal stiffness, in particular a high ring stiffness, and a low drag.